I tested in SW2016 SP3. It does save the backups from a Save All in the drawing after editing the model and not saving (watch the time stamp change on the backup files when you hit Save All). But I believe it comes down to how the Backup feature works in SOLIDWORKS that may make it appear that no backups are made.
If you open a Part file then make modifications and Save, the backup copy will not include these latest changes. The backup copy saved is the version of the last save (the version when you first opened the file). This is so you have a backup copy in the previous version before the changes that you just saved. If you save a second time without making any changes, the backup copy will update to match the current version because it's the same as version of the last save (since you didn't make any changes from the last save).
So therefore if you edit a Part file (but don't save), then switch to the Drawing and Save All, it's making the backup copy of the Part of the version prior to any of the changes (as discussed above). But if you do a second save in the drawing, it no longer prompts to Save All so the Part file doesn't get saved again to match the current version. But it will update the backup of the drawing (for example if you had added annotations to the drawing before the first Save All) since this is the second time saving the drawing.
If you save a second time without making any changes, the backup copy will update to match the current version because it's the same as version of the last save (since you didn't make any changes from the last save).
ahhh yes. this is what I did.
I didn't realize SW was doing exactly what I wanted it to do... save the old file prior to any changes I made... which means when I was looking for my files by date they wound up at the bottom of the list because they were from 2013. Duh. such a dummy.
And I only had 1 copy checked so it just overwrote the files as you said Scott.
If I had copies set to 10(because I make lots of mistakes saving what I shouldn't), my original file would have been there.
So user error, not SW error.